The Custom Tables extension allows you to create, manage, and display custom data on your Joomla site. It is helpful if you need to display data that is not part of the standard Joomla content structure. For example, you could use this extension to create a custom table for product information, customer data, or any other type of data that you need to display on your site. The Custom Tables is the CRUD solution for Joomla 3.x and 4.x - CREATE, READ, UPDATE and DELETE. You can add tables, fields, and layouts to create catalogs, forms, or details pages. It has 40 Field Types: Integer (numbers), Decimal, Text String, Time, Email, Color, Image, File, User, Language, etc.
felixkat
commented
2 years ago 
joomlaboat
commented
2 years ago
A table can be created using an underscore, i.e "this_table"
This name format is accepted but prevents records being added and causes SQL errors.
The code needs to either sanitise table names on creation or the SQL needs to cater for non alphanumeric characters.
Renaming the table by removing the underscore solves the issue.